1. Field of the Invention
The present invention relates generally to a multihop relay wireless communication system, and in particular, to an apparatus and method for selectively using a frame structure adequate for a system environment in the multihop relay wireless communication system.
2. Description of the Related Art
To enable rapid communications and accommodate more traffic, a fourth generation (4G) communication system includes cells having very small radius. The design of a centralized 4G communication system is proving difficult. In this respect, the 4G communication system needs to control and implement in a distributed manner and to actively cope with an environmental change such as joining of a new base station. That is, the 4G communication system requires a self-configurable wireless network capable of configuring a wireless network in an autonomous or distributed manner without the control of a central system.
In order to practically implement the self-configurable wireless network, the 4G communication system needs to adopt a technique applied to an ad-hoc network. In other words, the 4G communication system must realize the self-configurable wireless network by adopting a multihop relay scheme of the ad-hoc network to the wireless network including a stationary base station.
Since a typical wireless communication system communicates along a direct link between a stationary base station and a mobile station, it is quite easy to construct a radio communication link of high reliability between the mobile station and the base station. However, since the position of the base station is fixed in the wireless communication system, flexibility of the wireless network configuration is low. Thus, in the wireless environment under the severe change of traffic distribution or traffic requirement, the wireless communication system has difficulty in providing efficient services.
To overcome those shortcomings, the wireless communication system can make use of a relay service which transfers data on multiple hops via neighboring mobile stations or relay stations. The relay wireless communication system is able to rapidly reconfigure the network with respect to the communication environment change and to more efficiently operate the entire network. By establishing a multihop relay path via the relay station between the base station and the mobile station, the wireless communication system can provide a radio channel of far better channel condition to the mobile station. In a cell boundary under the unfavorable channel condition from the base station, the wireless communication system can provide the rapid data channel and expand the cell coverage area by use of the multihop relay scheme via the relay station.
FIG. 1 illustrates a general multihop relay wireless communication system.
A Base Station (BS) 100 in FIG. 1 is connected to a Mobile Station (MS) 110 in a service coverage area 101 by a direct link. In contrast, the BS 100 is connected to an MS 120, which travels outside the service coverage area 101 in the bad channel condition, by a relay link via a Relay Station (RS) 130.
The BS 100 can communicate with MSs, which travel in the outskirts of the service coverage area 101 or in a shadow area under the severe shielding by buildings in the hostile channel condition, by way of the RS 130. To relay signals between the BS and the MS via the RS, the wireless communication system needs to establish not only a BS-MS link but a BS-RS link and an RS-MS link.
However, since the conventional wireless communication system does not take into account the RS, the conventional wireless communication system does not allocate resources for the BS-RS link and the RS-MS link as shown in FIG. 2. FIG. 2 depicts a frame structure of an Institute of Electrical and Electronics Engineers (IEEE) 802.16e system.
The frame structure of the conventional wireless communication system is shown in FIG. 2.
The frame of FIG. 2 includes a DownLink (DL) subframe 200 and an UpLink (UL) subframe 210.
The DL subframe 200 includes a sync channel, control information, and a DL burst transmitted from the BS to the MS.
The UL subframe 210 includes control information and an UL burst transmitted from the MS to the BS.
As discussed above, not considering the RS, the conventional wireless communication system allocates the resources merely for the BS-MS link. To adopt the multihop relay scheme, the wireless communication system requires a frame structure which allocates the resources to not only the BS-MS link but also the BS-RS link and the RS-MS link.